1. Field of the Invention
The present invention relates to a mounting structure for an LSI suitable for use in mounting a bare LSI chip on a printed circuit board.
2. Description of the Related Art
Conventionally, a bare LSI (Large Scale Integrated Circuit) chip was mounted on a substrate having a thermal expansion coefficient relatively close to that of the chip, e.g., on a ceramic substrate (its thermal expansion coefficient is within the range of 7 to 9 ppm). In recent years, however, for the purpose of lowering prices, there has been established the technology of mounting a bare LSI chip on a build-up substrate employing a printed circuit board.
However, since the thermal expansion coefficients printed circuit boards is within the range of about 14 to about 16 ppm which is larger than those of ceramic substrates and also the printed circuit boards is softer than any of the ceramic substrates, when connecting an LSI to a printed circuit board, the reliability in connection backed by the temperature cycling tests and the like can not be ensured due to occurrence of the In the worst scenario, the LSI may be damaged cases.
Then, while there has been adopted the technique of filling the gap defined between an LSI and a printed circuit board with resin to integrate the LSI and the printed circuit board with each other in order to ensure the connection reliability, in this case as well, there are many limits in terms of materials of resin, the size of an LSI and the like.
In particular, when the size of an LSI is increased, the difference in the thermal expansion coefficient between the LSI and the printed circuit board is large though the LSI and the printed circuit board are integrated with each other by filling the gap defined therebetween with resin, and hence the occurrence of the warpage due to the bimetal effect can not be prevented. When the warpage occurs, this exerts a bad influence on the connection reliability of the LSI, and also if the warpage exerts an influence on the overall printed circuit board, then this will exert in turn a bad influence on the reliability of other components.
In addition, since the amount of calorification is increased when the size of the LSI is increased, a heat sink is required. However, since the printed circuit board itself is thin and does not have the durability enough to support the heat sink, which is heavy for the printed circuit board, it is impossible to apply any of good way of heat sinking the printed circuit board.
Heretofore, while there has been known the method of fixing a heat sink employing the stiffener on the rear face of the printed circuit board in order to fix the heat sink such as an LGA (Land Grid Array) or a BGA, it is impossible to obtain the sufficient effect.
In the light of the foregoing, the present invention was made in order to solve the above-mentioned problems associated with the prior art, and it is therefore an object of the present invention to provide a mounting structure for an LSI mounting, which structure is capable of removing any of the disadvantages as described above to improve the reliability in connection between an LSI and a printed circuit board and capable of holding a heat sink without any of difficulties.